This invention relates to methods and apparatus for treating large flows of recirculated water (e.g. 30 to 60 gallons/min.), such as swimming pool or spa water to eliminate the need for chemical treatment. A further aspect of this invention relates to purification of potable water at the same rates (e.g. 30 to 60 gallons/min.), as are associated with the water supply from a well or city, county municipal to a residential or commercial building.
The use of germicidal ultraviolet tubes in treating swimming pool water has been proposed, and is described for example in Dadd U.S. Pat. No. 4,230,571, issued Oct. 28, 1980 and Kaas U.S. Pat. No. 4,372,860, issued Feb. 8, 1983, and similar devices for treatment of potable water are described in Beitzel U.S. Pat. No. 4,273,660, issued June 16, 1981 and Lewis U.S. Pat. No. 4,255,663, issued Mar. 10, 1981.
In these earlier proposals, an ultraviolet tube was inserted into a quartz tube or some other surrounding housing, the water to be treated flowing through a flow passage on the outside of the quartz tube. The Lewis patent discusses using bactericidal UV irradiation at 253.7 nm. and ozone creating irradiation at about 188 nm., and recognizes that elimination of a quartz jacket or sheath will eliminate some problems associated with such a sheath, but may, by heat transfer from cold water, lower the operating temperature of the UV tube below optimum. Lewis thus discloses a solution to the problem as thus viewed, by providing a double wall tube incorporated in a disposable UV irradiating unit. In Beitzel U.S. Pat. No. 4,273,660, a flow of air is introduced between the tube and such housing to cause production of ozone which is then directed into the flow of water.
In either case, the ultraviolet tube was thus separated from direct contact with the water flow, which inevitably attenuates the effective irradiation of the water. When gaseous ozone is injected by venturi or otherwise into a flow of water, the tendency is for the ozone to "bubble out" of the water, not mix into the water, thus making it difficult if not impossible to maintain any residual ozone in the water. Thus, although this type of treatment will provide a certain degree of purification, supplemental chlorination of the water may still be required due to erratic irradiation or ineffectiveness in mixing sufficient quantities of ozone into the water. This makes these methods unattractive as an alternative to chlorination, particularly where there is a need to treat a substantial flow of water, as is associated with a water supply from a well to a residence or small business, or with a pool, spa, or cooling tower where the substantial quantity of water is recirculated..
U.S. Pat. No. 4,069,153 issued Jan. 17, 1978 to Gunther describes a system of providing a continuously available source of "physiologically safe" water, for use in fluid therapy, using an ultra-violet light emitting lamp with a special quartz shield, whereby UV light is radiated into a flow of water in the range of 180 to 200 nm. to convert dissolved oxygen into ozone; all of the water is required to flow within 6 mm. of the lamp surface. This, of course, greatly reduces the flow capacity of such a system, to the point where it is impractical for treating large flows such as mentioned above.
There is an observed tendency for the surface of a UV lamp and quartz sheath, which is exposed directly to water being treated, to become coated with a scum-like layer of deposits, such as calcium related particles, which will tend to build up to the point that there is intererence with the transmission of ultraviolet light into the surrounding water. Also, such UV lamps are designed to operate at about 80.degree. F., and exposure of the lamp while operating to lower water temperatures will cool the lamp and reduce the amount of ultraviolet light emission from the lamp. Thus, a successful and acceptable system utilizing UV water treatment must include provisions for quick and easy maintenance of the UV lamps, such as cleaning their surfaces as needed, or otherwise reducing the deposits remaining on those surfaces, and must also compensate for the tendency to reduced UV emission with lowering of lamp operating temperature.
Also, such prior art arrangements and methods do not provide sufficient control over the growth of algae in the pools, and it is well known that suppression of algae growth, particularly on pool walls, and especially in warm climates with substantial sunshine, represents a further difficult control problem. This is particularly true of owners of private pools or spas who are unskilled in (and do not wish to be bothered by) the chemical regulation techniques necessary to maintain clear algae free, very low bacteria content water in their pools.
U.S. Pat. No. 4,492,618 issued Jan. 8, 1985 to Eder, discloses a method of disinfecting pool water using sacrificial copper-silver (Cu-Ag) alloy electrodes connected to a polarity reversible power source, but that method also requires the addition of quantities of sodium persulfate into the water, and does not recognize the advantages of using ozone to purify the water.
Accordingly, there is a need for a device and a method of treating a substantial flow of water, making use of one or more ultraviolet tubes or lamps, for direct bactericidal irradiation treatment and for converting dissolved oxygen in the water into substantial amounts of ozone which result in residual ozone treatment of the water for some hours when the purification device is switching off. Such a device and method must include provisions for easy UV lamp maintenance, an extended period of time between necessary cleaning and maintenance, and compensation for the tendency to reduced UV output from the lamps when operating temperatures may decrease below optimum. This need exists in purifying potable water and, when combined with a regulated source of copper ions, to eliminate the need for supplementary chlorination or other chemical treatment in large recirculating flows of water such as in swimming pools and spas.